1. Field of the Invention
The present invention relates to an electron detector for efficiently detecting backscattered electrons in electron beam apparatuses such as electron microscopes.
2. Prior Art
Backscattered electron detectors used in electron beam apparatuses such as electron microscopes are available in two types: one using semiconductors and one using scintillators. An example of the backscattered electron detector of the scintillator type is shown in FIG. 1.
In the backscattered electron detector shown in FIG. 1, an objective lens 2 is disposed in the upper part of a specimen chamber 1 of an electron microscope. A focused electron beam 3 passing through the objective lens 2 is radiated against a specimen 4. Backscattered electrons 5 released from the specimen 4 strike an electron sensing portion 7 of a scintillator 6 coated with phosphor which emits light. The light thus emitted is detected by a backscattered electron detector 10 made up of a photomultiplier 8 and an amplifier 9.
Such a conventional scintillator 6, however, has the following drawback. The electron beam 3 that passes through a hole 6a formed in the scintillator 6, as shown in FIG. 2, irradiates the specimen 4, and the resulting backscattered electrons 5 strike the scintillator 6. Those backscattered electrons impinging on a scintillator base side 7a of the electron sensing portion 7 with respect to the hole 6a are collected and detected by the electron detector 10 with high efficiency. But light produced by those electrons that impinge on a scintillator end side 7b of the electron sensing portion 7 is reflected or scattered by the surface of the hole 6a and does not reach the photomultiplier 8, failing to be detected.
Since not whole area of the sensing portion 7 of the scintillator 6 can effectively arrest and detect the backscattered electrons 5 but only the scintillator base side 7a of the electron sensing portion 7 with respect to the hole 6a effectively captures the backscattered electrons, the overall detecting efficiency of the scintillator 6 is low and a significant improvement in the detection efficiency cannot be expected.